Such timing advance control has heretofore been accomplished in contact breaker type ignition systems by mechanical expedients as conventional centrifugally actuated advance and vacuum diaphragm actuator structures, which have been added to the ignition distributor to produce a progressive mechanical displacement of certain distributor components relative to the breaker points within the ignition distributor. With the advent of electronic breakerless or contactless ignition systems, it is desired to eliminate these mechanical timing control instrumentalities and to accomplish the requisite timing advance in an electronic manner for reasons of economy, simplification of the distributor structure and preciseness of timing control.
In one such ignition system as set forth in U.S. Pat. No. 3,314,407, electrical pulses developed by a pulse generator responsive to engine speed are used to produce an electrical signal of repeating sawtooth waveform and of a repetition rate related to engine speed. The sawtooth signal is integrated to derive a d.c. signal, which is equal to the peak value of the waveform and is inversely related to engine speed. The integrated signal is applied to an amplifier whose gain is chosen to be equal to or less than unity and whose output is compared to the repeating sawtooth waveform to derive a basic timing control or trigger signal for initiating the pulsing of a pulsed ignition system at a point or time related to the orientation of the pulse generator to the engine. The amplifier notably is of the variable gain variety whose gain is varied inversely in accordance with predetermined engine operating parameters, as speed and vacuum, to advance or vary the time of occurrence of the trigger signal for pulsing the ignition system.
In accordance with the present invention, an electronic spark advance timing control is provided for an electronic breakerless ignition system for an internal combustion engine wherein the timing control is provided by waveform comparison of a first electrical signal representing instantaneous engine rotational position and a second electrical signal of a substantially fixed level proportionally related to a predetermined firing angle. The occurrence of the firing event in advance of or retardation relative to the predetermined firing angle is affected by modulating one of said first and second electrical signals with one or more additional electrical signals each of which varies in accordance with a different engine operating parameter and is directly added to the signal to be modulated. The apparatus of the present invention generates a crankshaft position signal whose amplitude is independent of engine speed so as to avoid the need for a variable gain amplifier as well as the need for the peak position signal derivation as required by the prior art system and permits a plurality of timing modulation signals to be straight forwardly added to not only advance, but also to retard, the spark timing.
Another feature of the invention resides in the provision in the subject electronic spark timing advance controller of a fast warm-up control for catalytic or reactor-equipped emission controlled internal combustion engines. Present automotive catalysts and reactor systems require a minimum temperature, usually in excess of 1200.degree. F., for effective activity. This presents a problem during the engine warm-up period, since the catalyst or reactor cannot be immediately effective. The apparatus of the present invention decreases the warm-up time by increasing the heat rejection to the exhaust by operating the engine at retarded spark timing during the warm-up period, the retardation of the spark timing being accomplished electrically with the subject electronic spark timing control apparatus used to vary the spark timing of the engine.